Academic Discussion on the History and Theory of the Historical Sciences

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<7:82>From schoenem@QAL.Berkeley.Edu Tue Mar 22 02:30:32 1994
Date: Mon, 21 Mar 1994 22:17:36 -0800 (PST)
From: Tom Schoenemann <schoenem@QAL.Berkeley.Edu>
Subject: Re: Donnelly on TIME, fossils, and human origins
To: darwin-l@ukanaix.cc.ukans.edu
Regarding the possibility (or impossibility) of _H. erectus_ evolving
independently into _H. sapiens_, Chris Stringer and Peter Andrews (both
proponents of the "single origin" model, where _H. sapiens_ evolves first
in Africa ~150,000 years ago and replaces _H. erectus_ in the rest of the
world) listed the following "summary of suggested shared derived [i.e.,
unique] characteristics of _Homo sapiens_...":
In comparison to earlier _Homo_ species, _H. sapiens_ has:
1) a more gracile [i.e., more lightly built] skeleton,
2) a larger cranium
3) considerably reduced or absent supraorbital torus (i.e., "brow
ridges") and external cranial buttressing
4) reduced size of the dentition and supporting architecture
5) orthognathous face (face tucked under the anterior cranium)
6) a mental eminence (i.e., chin)
(This is from: Stringer, C.B. and Andrews, P., 1988, "Genetic and fossil
evidence for the origin of modern humans," _Science_ v.239:1263-1268.)
Now, these authors note that 5 may be related to 4, which I consider
reasonable. It has also been suggested that 6 is related to 4.
Furthermore, 1 and 3 are plausibly related to one another. It is not hard
to see these as one related complex - related in the sense that they all
are likely results of increased behavioral complexity, increased control
over the external environment, and a concomitant decrease in the amount of
stress placed on the body. Given that _H. erectus_ had a well developed
stone tool technology, and probably had mastered the use of fire, it does
not seem to me to be out of the question that a common selective sieve
would have been operating along the lines of:
[increasing control over the environment <-> increasing brain size] ->
decreasing robusticity (1,3,4,5,6 above).
The first part of this equation was probably operating no matter where a
population of _H. erectus_ was living, and thus the morphological
characteristics distinguishing _H. sapiens_ could, under this model, have
evolved independently. The fact that agriculture was independently
invented at least twice indicates that similar complex behavioral
adaptations (in the non-biological sense of the word) can occur
independently given similar selective seives.
P. Tom Schoenemann
Department of Anthropology
University of California, Berkeley
(schoenem@qal.berkeley.edu)